feat(types): add types for helper functions (#193)

Author: hmsk

Diff for: index.d.ts

@@ -1,4 +1,4 @@
-import { AxiosInstance, AxiosRequestConfig } from 'axios'
+import { AxiosInstance, AxiosRequestConfig, AxiosResponse } from 'axios'
 import Vue from 'vue'
 
 interface NuxtAxiosInstance extends AxiosInstance {
@@ -10,6 +10,15 @@ interface NuxtAxiosInstance extends AxiosInstance {
   $post<T = any>(url: string, data?: any, config?: AxiosRequestConfig): Promise<T>
   $put<T = any>(url: string, data?: any, config?: AxiosRequestConfig): Promise<T>
   $patch<T = any>(url: string, data?: any, config?: AxiosRequestConfig): Promise<T>
+
+  setHeader(name: string, value?: string | false, scopes?: string | string[]): void;
+  setToken(token: string | false, type?: string, scopes?: string | string[]): void;
+
+  onRequest(callback: (config: AxiosRequestConfig) => void): void;
+  onResponse<T = any>(callback: (response: AxiosResponse<T>) => void): void;
+  onError(callback: (error: AxiosError) => void): void;
+  onRequestError(callback: (error: AxiosError) => void): void;
+  onResponseErro(callback: (error: AxiosError) => void): void;
 }
 
 declare module 'vue/types/vue' {